The present invention relates to an electrical switch and, more particularly, to a snap-type or push-button type key switch, for an electronic calculator, a television, a video tape recorder, or the like, including a sheet provided with a plurality of domed members.
In a key input device for an electronic calculator, or the like, an improvement in the operation of the key input device is desirable. For example, when a key input is carried out, it is desirable that the key input can be judged by the user. Therefore, click-type key switches have been developed, so that the user feels a click at his or her fingertips when the key input device is depressed to input key information.
One example of the above click-type switches is disclosed in U.S. Pat. No. 3,932,722 by Akira Obata et al, entitled "PUSH BUTTON BODY FOR A PUSH-BUTTON SWITCH PROVIDING SNAP-ACTION OF THE SWITCH". It is impossible, however, to form a flat and thin type switch in the push button of Obata et al.
Another example of the above type of switches is disclosed in U.S. Pat. No. 3,590,195 by Driver Douglas Louis Ashton, entitled "OILCAN PUSHBUTTON SWITCH". FIG. 5 shows a sectional view of a pushbutton such as that disclosed in U.S. Pat. No. 3,590,195. A plate is designated by numeral 100, and insulative sheets are designated by numerals 101 and 102. A plurality of first key contacts 103 are provided on the insulative sheet 102. The insulative sheet 101 functions as a spacer. The plate 100 is formed with a plurality of domed members 104 and may be made of an insulative sheet or a conductive sheet. Each of a plurality of second contacts 105 are formed on the inner surface of the domed members 104. Each of the domed members 104 is opposite to each of the plurality of first key contacts 103 provided on the insulative sheet 102 so as to provide an electrical connecttion between one of the first contacts 103 and a corresponding one of the second contacts 105 when the domed member 104 is depressed. The insulative sheet 101 has openings therein at portions corresponding to the domed members 104. The plate 100, and the insulative sheets 101 and 102 are layered with respect to each other. A rivet 106 is provided to forcibly clip or connect the plate 100 to the insulative sheets 101 and 102.
If the plate 100 is the insulative plate of plastic film such as polyester, it is easy to form the key switch, but the durability of the switch is decreased. When a large number of key switching operations are carried out, the user may eventually be unable to feel the click.
If the plate 100 is the conductive sheet of metallic material, the durability of the key switch is improved, but the force caused by the up/down movements of the domed members cannot be removed and may cause stress to the flat portions at the edges of the domed member (namely, the connecting portion between the plate 100 and the insulative sheet 101). Accordingly, the operation load caused by the key switching increases. That switch cannot be employed in a flat and thin apparatus. As the domed members 104 are integrally provided to a single flat sheet, the shape of the sheet may be changed when forming the domed members 104, and may be distorted. In the switch of FIG. 5, the rivet 106 is provided for securely clipping the plate 100 to the insulative members 101 and 102 in addition to an adhesive. Therefore, additional members are required for a securable connection between the sheet 100 and the insulative sheets 101 and 102. If the rivet 106 is not provided, the peripheral portions of the domed members 104 are separated from the insulative sheet 102 in directions b and c when the domed member 104 is depressed in a direction a. The stability of the switch is thus decreased. In the switch of FIG. 5, some rivets 106 must be provided between the adjacent keys to prevent the sheet 101 from separating from the sheet 102.